High-voltage rectifier for supplying heavy currents and being started by a magnetic field



1968 A. l. NASTJUKHA ETAL 3,369,

HIGH-VOLTAGE RECTIFIER FOR SUPPLYING HEAVY CURRENTS AND BEING STARTED BYA MAGNETIC FIELD Filed Oct. 29, 1954 4 Sheets-Sheet 1 iv g p in;

UkB

1958 A. 1. NASTJUKHA ETAL 3,

HIGH-VOLTAGE RECTIFIER FOR SUPPLYING HEAVY CURRENTS AND BEING STARTED BYA MAGNETIC FIELD Filed Oct. 29, 1964 4 Sheets-Sheet 2 FIG. 3

1968 A. 1. NASTJUKHA ETAL 3,369,141

HIGH-IQLTAGEI RECTIFIER FOR SUPPLYING HEAVY CURRENTS AND BEING STARTEDBY A MAGNETIC FIELD Filed Oct. 29, 1964 4 Sheets-Sheet 5 1968 A.NASTJUKHA ETAL 3,369,141

HIGH-VOLTAGE RECTIFIER FOR SUPPLYING HEAVY CURRENTS AND BEING STARTED BYA MAGNETIC FIELD Filed Oct. 2 9, 1964 4 Sheets-Sheet 4 United StatesPatent 3,369,141 HIGH-VOLTAGE RECTIFIER FOR SUPPLYING HEAVY CURRENTS ANDBEING STARTED BY A MAGNETIC FIELD Alexandr Ivanovich Nastjukha, 4th Ul.Gktjabrjskogo polja 11, Apt. 15; Evgeny Alexandrovich Koltypin, 1stShchukinsky pr. 6, Apt. 88; and Pavel Alexandrovich Smirnov, Tikhvinskyper. 9, Apt. 9,2! of Moscow, U.S.S.R.

Filed Oct. 29, 1964, Ser. No. 407,469 9 Claims. (Cl. 313161) ABSTRACT OFTHE DISCLOSURE .A high-voltage rectifier for the supply of heavycurrents including an arrangement of an anode within a hollow cathodeand a source of a magnetic field having lines of force which intersectthe cathode twice without intersecting the anode.

This invention relates to electrical devices intended for convertinghigh voltage currents and, more particularly, relates to a method ofrectifying high-voltage heavy currents and to a device for therealization of said method, i.e. an arc valve with a cold cathode.

Certain essential disadvantages are inherent in known power mercury-arcrectifiers. While in many cases there is no need in the starting phasefor adjustment of such rectifiers, special ignition devices arenevertheless required for the operation. In excitrons, for instance,such an ignition device is an excitation are on auxiliary anodes,

said are consuming a considerable amount of electric power. Moreover,the excitation arc acting during an idle half-cycle reduces the backvoltage of the excitron. In the ignitron, an ignition device is anigniter usually made of semiconductor materials. The greatly variablecharacteristics of the igniter affect the normal rectifier operation. Inpractice, the service-life of an i-gnitron is entirely dependent uponthe service-life of the igniter. Moreover, it can be said in generalthat ignition devices are the most complex and unreliable elements ofmercury-arc rectifiers.

Another disadvantage of the mercury-arc rectifier is found in themercury-pool cathode. While it offers a number of merits, it createscertain difiiculties in the manufacturing of rectifiers, requires theintroduction of auxiliary screens into the rectifier chamber and makesrectifiers greatly responsive to temperature. That is why thetemperature of the operating rectifiers should be kept with the aid of atemperature controlling system at a given level within the close limitsthereof. Such system consumes large amounts of electric power. Withignitrons operating in pulsing circuits, the pool cathode limits therectifier current-carrying capacity to a value not exceeding 10 ka.

A glow-discharge device of the Phillips ion gage type was proposed to beused as a rectifier with a cold cathode, operating without preliminaryignition, said device comprising a cathode, a target and a ring anode,all placed in a magnetic field. This system of electrodes placed in amagnetic field has different discharge starting potentials with thereversing of the anode polarity. The use of such devices is greatlylimited, however, by some undesirable features inherent in theglow-discharge, namely by a considerable voltage drop during theconductive half cycle and a low magnitude of the rectified current, ofthe order of 10 milliamperes.

An object of the present invention is to provide a method forrectification of high voltage alternating currents.

Another object of the invention is to provide an arc valve with a coldcathode capable of rectifying high voltage heavy currents (as high assome hundreds of amperes) without the use of an ignition device.

With the foregoing and other objects in view, the present inventionconsists of a novel device, i.e. an arc valve with a cold cathode in amagnetic field, and a method of rectifying alternating currents.

The method of the electric current rectification and the principle ofoperation of the proposed are valve in a magnetic field are based on thesharp difference between the discharge starting potentials with thereverse polarity of electrodes forming a gas-discharge gap in a magneticfield, provided certain conditions are available. These conditions ariseif the shape of the electrodes and the configuration of the magneticfield are so selected that part of the magnetic lines of force in thedischarge gap twice intersects the cathode without passing through theanode. An alternate condition providing for the difference in startingpotentials is utilized in the known glow-discharge devices of thePhillips ion gage type.

The same phenomenon can be employed to initiate the low gas pressure aredischarge. If during the con ductive half cycle the potential of theanode attains the value of the starting potential, the dischargeimmediately takes the form of an arc with a low drop of voltage of sometens of volts, characteristic for this form. When the conductinghalf-cycle is over and the polarity of the electrodes has changed forthe reversed one, an arc discharge is not likely to occur.

The are valve employing a magnetic field and operating in the waydescribed hereinbefore comprises a metal cylindrical chamber serving asa hollow cathode with a fiat anode disposed inside said chamber. The arcvalve is placed in the magnetic field of a coaxial solenoid so that theabove mentioned condition concerning the dependence of the dischargestarting potential upon the polarity of the electrodes can be realized.The are valve is capable of rectifying alternating current without anignition device exciting an arc with the anode potentials beingcomparatively low (500-1000 v.) and depending on the magnetizing force,pressure, kind of gas and the shape and material of the cathode, saidrectifier withstanding at the same time a considerable back voltage (ofthe order of 10 kv.)

For operation in pulsing circuits, the valve may be provided with anignition device. Decreasing the magnetic field, it is possible to obtainsuch conditions when the arc discharge does not appear even with theanode being positive. In this case an insignificant additionalionization will bring to the breakdown of the discharge chamber of thearc valve. The additional ionization may be brought about by means of asmall hot tungsten cathode or by a low power boosting discharge in anauxiliary chamber which is located under the main chamber and iscommunicating with the latter through several narrow-bore passages, theauxiliary chamber being placed in the magnetic field of said solenoid.

Other objects and advantages of the present invention will be moreapparent from the following description taken in conjunction with theaccompanying drawings, wherein:

FIG. 1 illustrates the arrangement of electrodes in a magnetic field;

FIG. 2 graphically illustrates the starting potentialpressure dependencefor the electrodes arrangement of FIG. 1;

FIG. 3 is a cross section of an arc valve with the cold cathode placedin a magnetic field;

FIG. 4 illustrates an arc valve with the cold cathode placed in amagnetic field and with an auxiliary ignition chamber; and

FIG. illustrates an arc valve with the cold cathode placed in a magneticfield with a hot ignition filament.

The method proposed herein for alternating current rectification bymeans of an arc discharge gap between cold electrodes placed in amagnetic field is based on a fact that the magnetic field under certainconditions considerably reduces discharge starting potentials witheither polarity of the electrodes. If a certain system of electrodes(FIG. 1) is placed in a magnetic field so that part of the magneticlines (lines I and 11; FIG. 1) of force twice intersects one of theelectrodes, a cylindrical cathode made, for instance, as a cylindricalchamber without passing through the other-the anode made, for instance,as a disc-shaped electrode, then, with the anode being positive, apotential well for the electrons will appear in the space between theelectrodes, particularly in the zone of the magnetic lines of forcemarked with a circle (zone III, FIG. 1). In fact, the magnetic fieldprevents the electrons from escaping this zone and reaching the anode,and the electric field does not permit them to come to the cathode. Theelectrons perform an oscillatory motion along the magnetic lines offorce and drift in the intersecting electric and magnetic fields aboutthe axis of the system of electrodes. Moving in this zone for asufiiciently long period of time, the electrons ionize the gas evenunder low pressure conditions, provided that the length of their meanfree path is much greater than that of the gap between the electrodes.As a result, with the anode being positive, the discharge startingvoltage sharply drops. When the anode is negative, the electrons rapidlyleave the space between the electrodes for the positive cathode. In thiscase the electric strength of the gap is sufficiently high and isdefined by the left branch of the Paschen curve. FIG. 2 illustrates thedependence of the starting potential in the system of electrodes as inFIG. 1 upon the pressure (for the air) at various values of the magneticfield H. The continuous lines (for H =l60 oersteds, H =190 oersteds andH =220 oersteds) correspond to potentials of the positive anode and thedotted line to that of the negative anode respectively. With the anodebeing negative, a magnetic field of several hundred oersteds is of noinfluence upon the electric strength of the gap. As seen from FIG. 2,the value of the potential at which the glow discharge occurs dependsupon the magnetic field and upon the pressure. Besides, it also dependsupon the configuration of the magnetic field, the shape and material ofthe cathode and on the kind of gas.

The peculiar feature of the method to be claimed is that of the use ofan arc valve with a low drop of voltage. Though the chosen forms of theelectrodes and configuration of the magnetic field are not the onlypossible embodiments of the invention, they still provide a relativelylow discharge starting potential during the conductive half cycle withthe minimum (of the order of -20 oersteds) magnetic field within thezone of the anode. It is just the last circumstances that facilitate aquick and practically instantaneous glow-to-arc transition even atcurrents of about 10 a.

Since this are discharge can be effected at a low gas pressure, thecharged particles, after the discharge is over and the polarity of theelectrodes has been changed, recombine on the electrodes. The spacebetween the elec trodes becomes quickly de-ionized, the electricstrength is restored and the arc-back does not appear. The pressureafter passing of the current pulse does not increase, ex-

cept for a relatively short process of aging. Moreover, a 1

reduction of the gas pressure has been observed in the discharge chamberdue to the passage of the current pulse.

The invention will now be described in connection with a possibleembodiment of the device for realization of said method.

Cylindrical aluminum chamber 1 (FIG. 3) serving as a hollow cathode ofan arc valve is sealed on base 2 by means of rubber washer 3. Copperanode 5 cooled by water supplied through pipes 4a is inserted in thechamber via insulator 4. The magnetic field is generated by solenoid 6located coaxially under the base of the valve. The cathode is cooled byrunning water delivered to jacket 7. The gas is evacuated from thechamber through branch pipe 8. The pressure of gas, say air or hydrogen,is set by means of an adjustable needle valve through pipe 9. Thepressure is measured by thermocouple pressure gage 10.

For the operation of the arc valve in pulsing circuits, the apparatus isprovided with an ignition device. A modification of the valve with anauxiliary discharge serving as an ignition device is shown in FIG. 4.Auxiliary ignition chamber 11 is positioned under the main chamber 1 inthe magnetic field of solenoid 6 and communicates with the latterthrough narrow passage 12. Ring anode 13 is placed inside the ignitionchamber, said anode receiving the positive trigger pulse. To facilitatethe booster discharge, the gas pressure in the ignition chamber is set alittle higher due to the direct delivery of gas into said chamber.

FIG. 5 illustrates another modification of the arc valve design providedwith an ignition device made as a miniaturized hot cathode. A tungstenfilament 0.3 mm. thick insulated from the chamber is mountedeccentrically in base 2 of the valve. The recess in which hot ignitioncathode 14 is positioned is screened from the main discharge chamber bymetal grid 15. The filament is fed with a fixed positive bias and at themoment of ignition it is fed with a negative trigger pulse.

In the steady process of the rectification of industrial frequencycurrents the valve operates in the pressure range equal to (1 to 10) 10-mm. Hg. The magnetic field in the center of solenoid 6 is approximatelyoersteds and in the zone of anode 5 it drops to 10-20 oersteds. The peakvalue of the rectified industrial current is as high as 1000 a.

If the valve is cut into a choke-coil shorting circuit (crowbar) underthe same pressure and magnetic field conditions, it startsautomatically, when the voltage of inductance becomes positive,resulting in currents of the order of 50 ka. and more with the pulseduration being 10 milliseconds.

When the ignition occurs under the same pressure conditions but with alower intensity of the magnetic field, the valve during the pulseoperation can operate for an inductive load in a capacitor dischargecircuit. If the pulse duration equals 1 millisecond, the valve retainsthe property of unilateral conductivity with the peak currents 50 ka.and more and the voltage up to 10 kv. The pulse frequency in this dutyis equal to several cycles per second. During single switchings of thevalve the unilateral current conductivity thereof was noted to be risingup to 100 ka.

While the present invention has been described in connection with thepreferred embodiment thereof, it will be understood by those skilled inthe art that changes and modifications may be made without departingfrom the spirit and scope of the invention, and accordingly, all suchchanges and modifications which fall within the true spirit and scope ofthis invention are intended to be covered in the appended claims.

What is claimed is:

1. A high-voltage rectifier adapted for supplying heavy currents andcomprising a metal envelope defining a chamber and including a coldhollow cathode, an anode inside said chamber, and means to generate amagnetic field in said chamber such that magnetic lines of forcesintersect the cathode twice without passing through the anode.

2. A rectifier as claimed in claim 1, wherein the envelope iscylindrical and the said means is a solenoid coaxial with the envelope.

3. A rectifier as claimed in claim 2, wherein the anode is symmetricallydisposed within the chamber at the top of the latter and the solenoid islocated outside of and below the envelope.

4. A rectifier as claimed in claim 3 comprising auxiliary ignition meansbelow said envelope and encircled by said solenoid.

5. A rectifier as claimed in claim 4, wherein said auxiliary ignitionmeans is in communication with said chamber and includes a ringelectrode supported on said envelope.

6. A rectifier as claimed in claim 3, comprising auxili ary ignitionmeans within said chamber.

7. A rectifier as claimed in claim 6, wherein the envelope is providedwith a recess at the bottom thereof to accommodate said auxiliaryignition means which includes a hot filament in the recess and a metalgrid shielding the filament.

8. A rectifier as claimed in claim 3, wherein said anode is hollow,comprising means to supply a cooling medium into said anode and means tosupply a cooling medium around said cathode, said rectifier furtherincluding means 20 References Cited UNITED STATES PATENTS 2,217,18710/1940 Smith 313161 2,799,804 7/1957 Biondi 313-198 X FOREIGN PATENTS1,134,765 8/1962 Germany.

JAMES W. LAWRENCE, Primary Examiner.

C. R. CAMP-BELL, Assistant Examiner.

